A strange tale of oral sex, a knife fight and the most unlikely of pregnancies recently brought to light by the blogosphere has doctors touting the triumphant persistence of sperm.

In 1988, a 15-year-old girl living in the small southern African nation of Lesotho came to local doctors with all the symptoms of a woman in labor. But the doctors were quickly puzzled because, upon examination, she didn't have a vagina.

"Inspection of the vulva showed no vagina, only a shallow skin dimple," so doctors delivered a healthy baby boy via Caesarean, the authors wrote in a case report published in the British Journal of Obstetrics and Gynaecology.

Her birth defect -- called Mullerian agenesis or Mayer-Rokitansky-Küster-Hauser syndrome -- didn't necessarily surprise doctors, but her pregnancy did. Even the 15-year-old girl could not believe she was pregnant.

Yet by looking at her records the hospital staff realized the young woman was in the hospital 278 days earlier with a knife wound to her stomach. The average pregnancy lasts 280 days. After interviews, they gathered that "Just before she was stabbed in the abdomen she had practiced fellatio with her new boyfriend and was caught in the act by her former lover. The fight with knives ensued."

The girl arrived at the hospital with an empty stomach -- and therefore with little stomach acid around -- and doctors found two holes from a stab wound that opened her stomach up to her abdominal cavity. The case report said doctors washed her stomach out with a salt solution and stitched her up.

"A plausible explanation for this pregnancy is that spermatozoa gained access to the reproductive organs via the injured gastrointestinal tract," the authors wrote.

"Here's an unbelievable set of coincidences," said Dr. Richard Paulson, head of the University of Southern California Fertility Program in Los Angeles. "But it's totally plausible."

Although doctors know that sperm needs a low acid (high pH) environment to survive, and would likely die eventually in the low pH of stomach acid, doctors also said that sperm comes in a protective fluid: ejaculate, a nourishing medium meant to protect the sperm.

Besides, "out of hundreds of millions of sperm if you knock out 90 percent of them, you're still going to have tens of millions of sperm," said Dr. Peter Schlegel, chairman of urology at New York Presbyterian Hospital/Weill Cornell Medical Center in New York.

Paulson agreed.

"Sperm are pretty hardy," said Paulson, who pointed out that sperm must make it out of the acidic environment of the vagina before reaching more friendly territory at the cervix and in the uterus. Once in the abdominal wall, Paulson estimated that the sperm could survive for days.

"It's a long way from the stomach into the lower abdomen, it's a heck of a trip, but they made it," said Paulson. "You just need sperm somewhere in the area of an egg."

Paulson said in the early days of fertility treatments in the 1980s, doctors injected sperm in the lower abdomen hoping for the coincidental encounter with an egg. The procedure, called DIPI or direct intraperitoneal insemination, has largely been replaced by more effective methods.

The Lengths Sperm Can Travel

Schlegel pointed out that although fertilization typically takes place in the fallopian tubes, doctors know that sperm can normally swim up and out of the reproductive organs into the abdominal cavity.

"The sperm are naturally there at times, and eggs are naturally there," said Schlegel. "Eggs are released from the ovary, and they sort of dance around before they get taken up by the fallopian tube."

Sperm Can Swim Far in the Female Body

So it seems, Schlegel concluded, that the sperm could also be taken up by the fallopian tube, as could a fertilized egg.

But some doctors are still suspicious of, or at least bewildered by the tale. The girl's birth defect is well known and by age 15, doctors say most girls would have been doubling over in pain with an abdomen filled with menstrual fluid that cannot escape.

The menstrual fluid of several periods would make it even more unlikely for a pregnancy to occur.

"She'd have pain all the time and would have a stomach full of blood all the time, and would have to be operated on, or she would eventually die," said Dr. Sherman J. Silber, director of the infertility center of Saint Louis at St. Luke's Hospital in Missouri.

Dr. Howard A. Zacur, a reproductive endocrinologist at Johns Hopkins, also had doubts. "The case report here suffers from the fact that an individual with a completely obstructed vaginal outlet would have been expected to have blood accumulation in the vagina, and/or uterus," he wrote in an e-mail.

The authors of the report guessed a pregnancy could only be possible if the girl had ovulated once or at most twice before her pregnancy.

Whatever the true story of the woman, and her now grown son, Silber said it could send a message to ordinary couples planning pregnancy.

Why Doubt the Longevity of Sperm?

"This story is a crazy story, and there's no way to make sense of it," said Silber. "But the data on sperm is that normally it's quite good in an alkaline environment for two or three days -- that's why the average couple wastes a lot of energy when they're trying to get pregnant."

Silber said he sees many couples who buy into the idea that they should time sex to coincide with the woman's ovulation. But Silber said the remarkable survivability of sperm means most couples don't have to change their normal sex lives at all.

"The average American married couple tends to have sex two or three days a week," said Silber, author of "How to Get Pregnant."

If sperm can survive for two or three days, that means the average sex life of an American married couple results in living sperm swimming around the woman's body every single day of the week.

"The practice to check when you ovulate and not to have sex until you're ovulating is stupid," Silber said.

Silber said because ovulation calendars and methods to detect ovulation are somewhat inaccurate, couples could miss ovulation and have sex too late.

"Twelve hours after ovulation, the eggs aren't good any more. You want to have the sperm there ready and waiting for when you ovulated," said Silber. "It's absolutely true that sperm can last a long time."